The present invention relates in general terms to headlights of the so-called elliptical type for motor vehicles, and in particular a headlight of this type which is designed to produce a main beam.
An elliptical headlight comprises, mainly, a recuperating and concentrating reflector which is in the form of an ellipsoid and which has a first focal region in which a light source is placed, and a second focal region. The light source is for example the filament of an incandescent lamp or the arc of a discharge lamp, and the second focal region of the reflector is such that light issued from the light source, after being reflected on the reflector, forms in the second focal region a patch of concentrated light. Such a headlight also includes a convergent lens, which is typically of the planar-convex type, which is focused in the vicinity of the second focal region of the reflector and which is capable of projecting on the road the above mentioned light patch.
A headlight of the above type lends itself well to the production of a beam which is delimited by a top cut-off line, for example a dipped beam. For this purpose, a mask is arranged in the region of the light patch for partly masking (obscuring or occulting) the patch, so that the upper edge of the mask defines the required cut-off line in the beam projected forward from the vehicle.
Attempts have also been made to make use of a headlight of the above type to give a main beam, that is to say a beam which has a point of concentration in the axis of the road, but which also has a certain degree of width and a certain degree of thickness, for example a long-range driving beam. This requirement is not readily satisfied by a headlight of the above type, and the reasons for this will be explained below.
In the first place, because of the large quantity of light required on the axis of the road, the use of a reflector which has a comparatively large lamp hole in its base, for fitting the lamp in the reflector, poses a problem. In this connection, the presence of this lamp hole causes a dark zone, corresponding to the image of the lamp hole, to occur in the projected beam, since naturally the lamp hole recuperates no light.
In fact, in order to obtain the greatest possible amount of light in the axis of the road, it is desirable to have a front surface of the lens which is as large as possible with respect to the surface of the lamp hole. This becomes more difficult to achieve as, in general, there is a requirement to give the headlight a reduced height and width, and therefore to have a lens which is as small as possible. This small lens is one of the most significant advantages of this headlight technology, especially from the point of view of styling.
It is of course possible to try and reduce the size of the lamp hole, given that the means for fitting the lamp to the headlight are usually arranged at the level of the lamp base, so that the lamp hole has to have a large surface area.
One solution for reducing the size of the lamp hole consists in mounting the lamp further back in the general direction of emission of the light, so that only its bulb has to pass through the lamp hole, with the lamp base situated behind the hole. As a result, the size of the lamp hole can be reduced, even if a safety distance has to be provided around the bulb of the lamp for preventing undesirable heating of the reflector in that region.
It will be understood that the two problems set forth above lead to the focal distance of the reflector being short. In this connection, a short focal distance is the direct consequence, firstly, of minimising the lateral and vertical size of the headlight, and secondly, of the above mentioned retraction of the lamp with respect to the reflector, bringing the light source further back in the reflector.
This short focal distance causes the reflector to produce a concentrated light patch of considerable size because the light source is not a point. Typically, the light source is a cylinder of about 5 mm long and about 1 mm diameter.
One example of the appearance of the beam corresponding to the projection of this patch on the road is shown in FIG. 1 of the accompanying drawings. It will be understood that such a beam, because of its significant extent vertically below the axis of the road, will light the road very close to the vehicle, while being significantly uncomfortable visually in the distance.
One solution to overcome this disadvantage could consist in providing, in the region of the light patch before the latter is projected, a mask similar to those which are used in dipped or passing beams, but in a turned back position such that it will occult the light which illuminates the road too close to the vehicle. However, this solution would not be satisfactory from the point of view of the visual comfort of the driver, because it would lead to very high contrast at the level of an imaginary line situated on the road in front of the vehicle. In addition, this contrast would be detrimental to the use of the beam both as a plain main beam (i.e. one where the dipped or passing beam is extinguished), and as a main beam complementary to the dipped or passing beam which in that situation remains illuminated.
An object of the present invention is to overcome the above mentioned drawbacks and limitations in the present state of the art.
More precisely, the invention aims to propose means which are capable of ensuring progressive reduction of the amount of light, to the extent that this light illuminates zones of the road closer and closer to the vehicle.
Another object of the invention is to obtain this objective without giving rise to undesirable colouring effects in the light due to chromatic variations in the angles of refraction by the lens according to the wavelength of the light. In particular, the present invention aims to make use of the effects of masking the light at a distance from the focal surface of the lens. This focal surface would be a plane in a perfect lens, but for an imperfect lens such as a planar-spherical lens, it will be a sort of dome, the focus of which constitutes the apex. However, the invention also aims to ensure that, in spite of such defocalising of the mask, no undesirable colouring effects, i.e. the chromatic effects mentioned above, will be produced in the beam.
According to the invention, a headlight of the elliptical type for a motor vehicle, including a recuperating and concentrating reflector of the ellipsoidal type having a first focal region in which a light source is placed, and a second focal region in which a patch of concentrated light is formed after reflection of the light from the source by the reflector, and further including a convergent lens which is focused in the vicinity of the second focal region of the reflector, and which is capable of projecting the said patch of concentrated light on the road, the reflector and the lens defining an optical axis of the headlight, is characterised in that it further includes a mask adapted to obscure a part of the light passing between the reflector and the lens, being disposed entirely above the said second focal region and having at least two occulting regions which are spaced apart in the direction of the said optical axis, and each of which is adapted to obscure, simultaneously, a specific part of the light.
Further features of the invention, which are preferred but not limiting, and which may be applied to the invention alone or in any practicable combination, are as follows:
each of the said spaced-apart occulting regions defines a sharp edge;
each of the said spaced-apart occulting regions defines a curved edge;
the said spaced-apart occulting regions define a sharp edge and a curved edge respectively;
the two edges are at the same height;
the edges are at different heights;
a front edge is situated lower down than the rear edge;
one of the edges is situated substantially directly below a focus of the lens;
the edge situated substantially directly below the focus of the lens is the front edge;
the edges are situated behind and in front of the focus of the lens in the direction of the optical axis, respectively;
the edges are situated at substantially equal distances from the focus of the lens in the direction of the optical axis;
the mask has a third occulting region intermediate between the first and second occulting regions;
the said intermediate occulting region defines a sharp edge;
the said intermediate occulting region defines a rounded edge;
the edge defined by the said third intermediate occulting region is at substantially the same height as one of the said first and second occulting regions;
the edge formed by the said third intermediate occulting region is lower down than each of the said two occulting regions;
the mask extends in a direction which is generally horizontal and transverse to the optical axis, and has the same vertical cross section over its whole length;
the mask extends in a general direction which is horizontal and transverse to the optical axis, and has a vertical cross section which varies along its length;
the mask is made of bent sheet metal;
it is an autonomous main-beam headlight;
it is a main-beam headlight with a complementary dipped-beam headlight.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of some preferred embodiments of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.